Seifert, U. (Corresponding author) ; Institut für Festkörperforschung (Jülich) ; Universität (München)

1994
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Report No.: Juel-2997

Abstract: $\textbf{1.1 Vesciles}$ Membranes as studied in this treatise consist of a bilayer of lipid molecules that are composed of a hydrophilic head and two hydrophobic hydrocarbon chains. When introduced into an aqueous environment, these amphiphilic molecules aggregate spontaneously into two monomolecular layers held together by weak non-covalent forces due to the hydrophobic effect. These membranes form large encapsulating "bags" called vesicles because open sheet-like conformations would involve a large energy along the hydrophobic edges. Even though the membrane is only a few nanometers thick, the size of these vesicles can reach macroscopic dimensions of up to 100 micrometers. Video microscopy reveals both an extreme softness of the membrane since thermally excited shape fluctuations are strong enough to become visible and an amazing variety of different shapes, among which shape transformations can be induced by changing parameters like the temperature or osmotic conditions$^{1}$. Interest in these systems arises from at least three perspectives$^{2}$, emphasizing (i) the unique material properties of a fluid membrane resulting from its molecular architecture ($\textit{the physical chemistry}$ aspect), (ii) the enormous variety of conformations exhibited by membranes considered as two-dimensional surfaces ($\textit{the statistical physics}$ point of view), and (iii) the ubiquitousness of membranes in $\textit{biological}$ systems. Before we return to these aspects later in this introduction, a few examples will serve to introduce the physical object of this study. The most prominent example of a shape transformation is the budding transition shown in Fig. 1.1, where the shape change of an initially spherical vesicle is recorded with video [...]

Keyword(s): fluid ; membrane ; phase diagram ; fluctuation ; adhesion ; dynamics

1. Institut für Festkörperforschung (IFF)